Data storage devices, such as those that utilize disc-shaped data storage media like disc drives, record data in tracks on the data storage media and also read recorded data from the tracks. Devices do this by positioning a read/write head with a signal transducer over a track so that data can be written to or read from the track. Errors in reading or writing data can occur due to problems positioning the head or irregularities in the track and storage media. When an error occurs as data is written to or read from a track, a retry operation typically is performed in an attempt to correct the error. Retry operations often include a variety of retry procedures, also sometimes referred to as error recovery routines, each designed to correct for a different error type. If the retry operation is unsuccessful, i.e. none of the retry procedures were able to correct the error, the device interprets this as a “hard” error and considers that location on the track no longer usable.
On a data storage media a read error may occur due to various causes, such as scratches on the media, asperity (or roughness) of the storage media surface, and non-homogeneity in data storage material over the media. Read errors may also occur due to track “wander” wherein the track does not follow the expected path. Errors at different locations on the data storage media may be caused different things and, thus, require different retry procedures to correct. Additionally, errors may change over time. Errors may be introduced over time as the data storage media deteriorates with use and age or is damaged. Although rare, errors may also ameliorate over time as well.
Various retry procedures have been invented to correct for many of the errors encountered. These may include changing the gain of a reading or writing circuit, looking for data in the vicinity of where the track was expected to be found (off-track checking), and changing the bias value of a magneto resistance (MR) element in the case where the MR element is used as a read head. For example, in a disc drive with a magnetic disc and a hard-disc controller, the retry procedures may be, for example, varying an off-track quantity which is an offset quantity between the center of the magnetic head and the center of the track, varying a bias current value given to an MR element in the case where a magnetic head is equipped with the MR element, or various automatic gain control factors such as the gain of the variable gain amplifier (VGA) and the adaption rate of the finite impulse response (FIR) filter. Retry procedures also often include a number of subprocedures, comprising incrementally increasing some deviation from a normal read or write operation parameter such as location or bias.
The retry operation typically performs its retry procedures in sequence until the error is corrected or the procedures are exhausted and a hard error is determined. Depending on what type or error is at a location, the retry operation may take more or less time in correcting it because of where in the retry procedure sequence the appropriate retry procedure occurs. For example, an error may be track wander error, which will be corrected by the off-track retry procedure. If the off-track retry procedure is the first retry procedure in the retry procedure sequence, then the error will be corrected relatively quickly. However, if the off-track procedure is the last in the sequence, the retry operation—while still successful—will take a relatively longer time. Since the overall rate that data can be read and written is an important performance parameter for data storage devices, there is a need to minimize the amount of time a data storage devices spends performing retry operations.
Typical retry operations are standardized according the data storage device's characteristics at the design stage. The procedures and subprocedures of the operation are selected and ordered based on certification testing of a predefined population of the product prototype. The ordering of the procedures is made by sorting the retry procedures in the operation sequentially by probability of success, with the most probable retry procedure made the first procedure in the operation. While not optimum for every error on the tested media, when looking at the media as a whole, the sequence is optimized over the media as a whole, resulting in an optimized average time the device spends performing retry operations. The resulting standardized retry operation is stored in every device and is used without modification throughout the lifetime of the device. Whenever an error is detected that requires a retry, the retry operation starts with the first retry procedure and proceeds sequentially through its subprocedures. Then it proceeds to the second procedure and so on through all the procedures and subprocedures. If at any time a retry subprocedure is successful, then the retry operation is terminated. The implementation of the operation is simple and relatively fast, both during manufacture and operation. The standardized retry operation, however, does not take into account any individual variation among devices or the degradation of the device over time. For that reason, it is not very efficient at reducing the time a device spends performing retries.
Because the retry operation affects the average read and write speed of the device, there is a general need to minimize the average time a device spends performing retry operations. In addition, there is also a need to adjust the sequence as the device degrades over time and maintain the optimal sequence.
Accordingly there is a need for a smart method for performing retry operations that re-optimizes itself by adjusting to variations in errors over time and location in the storage media. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.